The present invention relates generally to measurement apparatuses and more particularly to an apparatus for acquiring pendulum oscillations crane loads using measurement techniques.
Cranes, such as container cranes, pick up loads at a predetermined location, transport them over a known distance, and set them down at an established location. In automating these operations, the problem occurs that the load is propelled into unwanted pendulum motions due to the necessary start-up and braking actions. These pendulum motions die out slowly due to the negligible inherent damping of the system. As a result, they considerably hinder and delay the process of accurately picking up and lowering loads. Since the conveying capacity is determined to a large extent by how fast the load can be picked up and placed down, to provide the capability of a large conveying capacity, one must attempt to control these motions using automatic control engineering measures, to reduce them to a tolerable level or even to utilize them. When the pendulum motion of the load cannot be easily calculated in advance, such as by computer simulation, one must be able to detect the actual pendulum motion. Thus, the actual position of the load changing as a function of time must be determined to compensate for the pendulum oscillations of the load as well as to automatically control the positioning of the load.
However, this problem has only been partially solved in known methods heretofore. Thus, according to existing mechanical methods, the swinging cables, on which the load is suspended, move metal bars that are arranged below the cable guide block, or rather cable drum. Such a mechanism allows the instantaneous swing angle or rather its rate of change to be acquired to compensate for the pendulum oscillation of the load with sufficient accuracy. However, the accuracy achieved by these mechanisms does not suffice for automatic load-positioning control systems. Moreover, the known system is mechanically sensitive and entails high maintenance costs.
It has been proposed to acquire the mentioned quantities with the aid of laser technology, by mounting laser-based scanning and ranging devices on the crane to scan the outer edges of the load within a specified angular scanning range. However, the current state of the art does not yet make it possible to simultaneously achieve very high measuring accuracies and short measuring times over a larger angular scanning range. To obtain a high measuring accuracy within still tolerable measuring times, the angular scanning range must be limited to a few degrees. The inherent danger is, however, that the load will disappear from the field of view of the laser-based scanning and ranging devices, given larger pendulum motions.
The present invention is directed to the problem of developing an apparatus for acquiring pendulum oscillations of loads borne by cranes with a high degree of accuracy and reliability.